Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $233.91   6.862%   $249.9609   $249.96   $249.95   $250.00  
  Purchase #2 $203.51   12.279%   $228.499   $228.50   $228.50   $228.50  
  Purchase #3 $241.75   10.615%   $267.4118   $267.41   $267.40   $267.40  
  Purchase #4 $75.66   11.806%   $84.5924   $84.59   $84.60   $84.60  
  Purchase #5 $211.62   5.333%   $222.9057   $222.91   $222.90   $222.90  
  Purchase #6 $160.70   4.289%   $167.5924   $167.59   $167.60   $167.60  
  Purchase #7 $197.81   7.686%   $213.0137   $213.01   $213.00   $213.00  
  7 purchase totals = $1,324.96       $1,433.9759   $1,433.97   $1,433.95   $1,434.00